The ongoing clinical care provided to patients with implantable cardiac device systems often includes the use of surface electrocardiograms (ECG). An ECG is a highly useful diagnostic aid for clinicians for the study of heart rate and rhythm. The ECG indicates the propagation of low amplitude electrical signals, commonly referred to as the cardiac impulse, across the myocardium giving information about depolarization and repolarization characteristics of the heart.
An ECG typically receives signals from a plurality of electrodes (3, 5, and 12 are common numbers) that are placed on the patient's skin surface. The ECG monitors voltage signals appearing between various pairs of the electrodes and performs a vector analysis of the resultant signal pairs to prepare various two-dimensional voltage-time graphs indicative of internal cardiac activity. Surface ECG refers to placement of electrodes on the surface, or skin, of the patient as opposed to directly to cardiac tissue which obviously requires an invasive procedure.
A programmer is a device that enables a clinician to telemetrically communicate with an implantable cardiac device such as pacemaker or defibrillator. Implantable devices often monitor and record a variety of internal physiological parameters of the patient and are often provided with a telemetry system to telemetrically transmit those measured and recorded parameters outside the patient's body. Implantable devices are also often capable of receiving telemetric signals to induce the device to set or change a variety of operational parameters of the device as well as to select among the physiological parameters that the device monitors and records. These parameters are often desirably changed during the implantation period to adjust the therapy provided and/or physiological parameters monitored in order to provide the attending clinician with different information or to adapt the therapy to a more efficacious regimen. It is highly desirable to set these parameters without the expense and health risks to the patient of an invasive procedure. The programmer enables the attending clinician to perform these tasks in a non-invasive, telegraphic manner.
A surface ECG is often used along with the programmer as the surface ECG provides additional information above that provided by the internal measurements obtained by the implantable device. The programmer is typically adapted to obtain a surface ECG through a special cable that generally interconnects the programmer to electrodes placed on the patient. As the programmer is thus electrically coupled to the patient, it is subject to exposure to electromagnetic interference (EMI) that may surround the interconnection. The programmer is also potentially subject to large common-mode 50/60 Hz (supply line frequency) signals that are picked up by the patient's body. Both EMI and common-mode signals degrade the accuracy of the ECG signal.
An additional concern in certain applications where defibrillation may be applied to the patient is the relatively large amplitude (hundred volt to kilovolt range) shocks that are typically applied to interrupt the fibrillation. These high voltage shocks can be conducted through other cabling interconnecting the patient and other equipment such as programmers. Accordingly, the front-end electronics (those directly in contact with the cabling) of the programmer generally require voltage protection adequate to prevent damage from up to 5000V that may be applied to the patient as defibrillation. The inclusion of such protection circuitry increases the cost and complexity of programmers.
The interconnection cable employed in prior art programmers with surface ECG systems presents some further difficulties in use for the clinician and for the patient. The cable is physically attached to the patient and impairs their movement in bed and can become entangled with bedding, I.V. tubes, etc. The cables also physically interconnect the programmer to the patient and thus present a physical obstacle that must be avoided by people moving in the room. The cables present a tripping hazard as well as a potential cause of upset and damage to the programmer or other devices that may be placed on tables or carts.
Another disadvantage of present programmer/ECG systems is that the clinician must physically connect the programmer to surface electrodes with the interconnection cable each time he visits a new patient. Often an individual programmer is not available for each patient due to cost considerations and the clinician must move a single programmer with him as he visits patients. It can be appreciated that disconnecting and reconnecting the cables each time a clinician visits a patient consumes the doctor's valuable time as well as presents a cause of wear and tear on the cables and connectors.
From the foregoing it can be appreciated that there is an ongoing need for a programmer/ECG system that reduces the need for obtrusive and hazardous cables. There is also a need for a system that facilitates movement of the clinician from patient to patient in different locations and maintains the functionality of programmers in communication with surface ECGs without the expense of providing a dedicated programmer at each patient location.